Messages

The pressure of the liquid-phase contains a large error (because of the strong molecular interactions). Usually people take the gas-phase value after the simulation is equilibrated.

I copied your input, and see no problems.
Have you tried to run it with zero cycles? Does it finish? is the output precisely (pseudo-atoms, force field etc) exactly what you put in?
If that works, run it with 10 cycles and see if it works.

One thing that could go wrong is that your input files are not ascci-files, but utf8 or windows-files that contain different newlines.
With utilities like 'dos2unix' and 'unix2dos' you convert between windows and linux/Mac.

You're swapping molecules in and out, and hence use the grand-canonical ensemble. In this ensemble, you fix the chemical potential (via the pressure/fugacity) and the amount of molecules fluctuates. So you're not able to control how many of where the molecules are. But that is the nature of adsorption.


Btw. you're missing a rotation move (although you could say this is also achieved via insertion of molecules, this is much less efficient).

MD always uses a shifted potential. Did you use the same in the Monte Carlo?
Did you use appropriate MC moves like translation, rotation, reinsertion, partial reinsertion to sample to the phase-space properly?

RASPA is not a parallel code. There is usually very little reason to in Monte Carlo. Once your system is equilibrated, you can start several independent jobs and just average the results.

There is a example in: examples/Tutorial/AdsorptionN2InMIL-47/3-Surface-area

Output:

Average Surface Area:
=====================
        Block[ 0] 252.784946 [-]
        Block[ 1] 253.629130 [-]
        Block[ 2] 253.098236 [-]
        Block[ 3] 254.806589 [-]
        Block[ 4] 253.473192 [-]
        ------------------------------------------------------------------------------
        Average surface area:   253.558418 +/- 1.379919 [A^2]
                                1652.157533 +/- 8.991397 [m^2/g]
                                1652.766655 +/- 8.99471 [m^2/cm^3]

The radii are used to compute bonding in flexible frameworks.
For small rigid molecules you define the relative positions of all atoms (including for example dummy atoms).

Yes, when FugacityCoefficient is set to 1.0, then ExternalPressure is the fugacity which you input.

I have not used that in many, many years. I am not sure that is working properly. You could check the source code.

Recheck how you use the charges, whether you use them from the 'pseudo_atoms.def' files or whether you use them directly from the CIF-file.

When you have negative excess adsorption, you crossed the vapor pressure according to the Peng-Robinson equation of state are inputted from the critical constants in the molecule file.
So either that is inaccurate, or your force field parameters of the molecule does not reproduces that vapor pressure.

The positions are relative to each other. In the output file you can see that it reorients the molecule anyway (according to the matrix of inertia).

With the current version of iRASPA for windows (1.1.18) you should be able to create movies (h265, h265, or vp9).

Visualize using what program? You need a program that can import multiple files are the same time.

Yes, it is possible to get similar values for absolute and excess adsorption, for example at low loading.
The difference gets larger for small molecules at high pressure.

There is nothing wrong. Check and read the manual for the tutorial 8.1. Here, the enthalpy of adsorption at infinite dilution is computed from the total energies (and not from the fluctuation formula).